Yahoo's 2013 data breach hit all three billion user accounts

Yahoo’s entire user base of more than three billion people were affected by Yahoo’s colossal data hack in 2013, despite initial reports limiting the damage to just one billion members.

The 2013 hack came to light amongst similar data breach revelations last year, years after the breach originally happened.

After Verizon acquired Yahoo for $4.5 billion, the company further investigated the issue. New intelligence revealed that although the breach was bigger than first suspected, it is not a ‘new’ security issue. Yahoo is sending emails to affected user accounts.

“The investigation indicates that the user account information that was stolen did not include passwords in clear text, payment card data, or bank account information. The company is continuing to work closely with law enforcement,” says a statement from Oath, a Verizon subsidiary.

Last year Yahoo advised users affected by the 2013, 2014 and 2015 breaches to change their passwords.

“Online intrusions and thefts by state-sponsored actors have become increasingly common across the technology industry. Yahoo and other companies have launched programs to detect and notify users when a company strongly suspects that a state-sponsored actor has targeted an account,” Yahoo said in a press release in September 2016.

"It’s nearly impossible for any organization to detect unauthorized, encrypted traffic coming in or out of their network unless they have strong cryptography practices. It’s also entirely possible that the attackers that perpetrated the 2013 breach retained access to the Yahoo! network and attacked again in 2014."

"This access would allow the perpetrators to empty the bank vault without anyone noticing. Unfortunately, Yahoo’s cryptography practices are not unusual. Undetected exfiltration of large amounts of data is a symptom of weak cryptography practices. We see this in nearly every major data breach.”

In addition to the three billion accounts affected by the 2013 breach, a second breach happened in 2014, which affected 500 million accounts. In 2016, details emerged of a breach from 2015 that compromised 200 million accounts.

The company also invalidated unencrypted security questions and answers so they could not be used to access accounts.

"Verizon is committed to the highest standards of accountability and transparency, and we proactively work to ensure the safety and security of our users and networks in an evolving landscape of online threats," comments Verizon CISO Chandra McMahon.

"Our investment in Yahoo is allowing that team to continue to take significant steps to enhance their security, as well as benefit from Verizon's experience and resources."

Venafi believes that a number of Yahoo's security certificates had not been reissued since January 2015. On top of that, the company used MDA5, which can be reversed through brute force attacks. Yahoo also used another hashing algorithm, SHA-1, which is no longer considered secure against state-sponsored attacks.

Last year Yahoo CEO Marissa Mayer dedicated her annual bonus to her employees in the wake of the breach fallouts.

“I am the CEO of the company and since this incident happened during my tenure, I have agreed to forgo my annual bonus and my annual equity grant this year and have expressed my desire that my bonus be redistributed to our company’s hardworking employees, who contributed so much to Yahoo’s success in 2016,” she said at the time.

In June 2017, Mayer stepped down as CEO. She received $23 million as part of her severance package.